Phosphoribosylanthranilate transferase (PAT) catalyzes the second step of the tryptophan biosynthetic pathway and is encoded by a single-copy gene that complements all the visible phenotypes of the tryptophan mutant (trp1-100) of Arabidopsis. The trp1-100 is blue fluorescent under UV light becuase it accumulates anthranilate. To obtain a plant with reduced PAT activity, PAT1 genes with several internal deletions in different promoter regions (pHS 101, pHS102, pHS104, pHS105, and pHS107) were induced into trp1-100 via Agrobacterium. Then, homozygous T3 plants were isolated and examined for blue fluorescence. Introduction of the PAT1 gene fusants results in the reversion of fluorescence phenotype except in the case of pHS105. These results prompted us to perform a parallel analysis of anthranilate synthase and PAT interms of the genetic complementation. A plant line carrying pHS105 gene fusant does not completely complement the blue fluorescence but it accumulates less anthranilate than trp1-100. The activity of PAT was reduced in the transgenic mutant as well. The plant carrying these constructs will add to the growing collection of molecular tools for the study of the indolic secondary metabolism.